This invention relates to toner particulates and toner compositions comprising particulates. More particularly, the invention relates to toner particulates comprising a styrene/acrylic copolymer having a first aliphatic hydrocarbon wax incorporated in the copolymer during polymerization, and a second aliphatic hydrocarbon wax mixed with the copolymer.
Numerous methods and apparatus for electrophotography, electrostatic recording and electrostatic printing are known in the art. Typically, a charged photosensitive surface, for example, a charged photosensitive drum, is irradiated with an optical image and an electrostatic latent image is formed on the photosensitive surface. In the development process, a developing agent, i.e. toner, is added to the electrostatic latent image.
Typically, toner is fed to a developer roller by a metering blade positioned against the surface of the developing roller. The developing roller, with the toner on its surface, is typically rotated in a direction opposite to that of the photosensitive drum, and the toner adheres to the electrostatic latent image to develop the image.
Various toner compositions have been developed in order to provide improved copying, recording and/or printing with such apparatus. The toner may be applied as a dry powder or may be applied from a liquid. When applied from a liquid, the liquid portion does not transfer to the substrate in large amounts and solid toner particles carried by the liquid form a dry or damp powder image. To bind the toner image to the substrate, one or more steps are taken, known collectively as fixing the image. Although various ways of fixing are known, such as the application of solvent, fixing by heat is a predominant technique employed in current technology. Fixing by heat avoids the addition of new materials to the system, which are a separate expense and which must be kept out of the atmosphere or otherwise kept from being an environmental hazard to users.
However, heat fixing does not necessarily bind the powder firmly into the substrate and does not necessarily preserve the fixed image over time. It has been found that styrene/acrylic resin-based toners do not exhibit equivalent fuse grade, which is resistance to rubbing and scratching, of a polyester-based toner at low fusing temperatures. However, the polyester-based toner is more expensive than a styrene/acrylic resin-based toners.
Unfortunately, many less expensive toner compositions have unacceptable fuse grade, thereby decreasing the print quality of the printer. Accordingly, a need exists to develop toners with improved fuse grade at lower costs than polyester-based toners while maintaining good print quality.
Accordingly, it is the object of this invention to provide improved toner particulates and toner compositions.
One aspect of the present invention is a toner particulate. The toner particulate comprises a styrene/acrylic copolymer having a first aliphatic hydrocarbon wax incorporated therein during polymerization of the copolymer, and a second aliphatic hydrocarbon wax mixed with the copolymer.
Another aspect of the present invention is a toner particulate made by the process of incorporating a first aliphatic hydrocarbon wax during polymerization of a styrene/acrylic copolymer and mixing a second aliphatic hydrocarbon wax with the copolymer after polymerization of the copolymer.
The toner particulates may be manufactured at relatively low cost and exhibit good fuse grade. Still other objects, advantages and novel features of the present invention will become apparent to those skilled in the art from the following detailed description, which is simply by way of illustration, various modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different obvious aspects, all without departing from the invention. Accordingly, the description is illustrative in nature and not restrictive.
The present invention relates to toner particulates and toner compositions comprising a styrene/acrylic copolymer having a first aliphatic hydrocarbon wax incorporated therein during polymerization of the copolymer, and a second aliphatic hydrocarbon wax mixed during the extrusion process with the copolymer.
The toner particulate comprises a styrene/acrylic polymer. As used herein, xe2x80x9cstyrene/acrylic polymerxe2x80x9d refers to polymers formed from styrene monomer and acrylic monomer. Suitable acrylic monomers include, but are not limited to, acrylic acid, and acrylates thereof, for example, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, and phenyl acrylate, methacrylic acid, and methacrylates thereof, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and octyl methacrylate, acrylonitrile, methacrylonitrile, and acrylamide. Suitable styrene monomers include styrene, and substituted styrenes, including, but not limited to, alphamethyl styrene, parachlorosytrene, vinyl toluene and divinyl benzene.
Polymers typically exhibit a softening temperature and a flow temperature. As used herein, xe2x80x9csoftening temperaturexe2x80x9d is intended to refer to the temperature at which particle collapse begins, and xe2x80x9cflow temperaturexe2x80x9d is intended to refer to the temperature at which the polymer achieves sufficient liquidity to be extruded in a capillary rheometer. The softening temperature and flow temperature can be determined using rheometers such as the SHIMADZU(trademark) capillary rheometer.
The polymers for use in the toner particulates may include a cross-linking agent in an amount of from about 0.01 to about 5 parts by weight per 100 parts by weight of the monomers employed therein. Conventional cross-linking agents may be used. In one embodiment, the toner comprises a resin which is free of cross-linking agents.
Toner particulates may comprise more than one polymer. Generally, the polymers will have a glass transition temperature of no less than 55xc2x0 C. In one embodiment, the particulate comprises a first polymer and a second polymer, each having a glass transition temperature of no less than about 55xc2x0 C., preferably no less than about 60xc2x0 C. Generally, the polymers will have molecular weights greater than about 2000.
In one embodiment, the toner particulate may comprise a first low molecular weight polymer and a second high molecular weight polymer.
The toner particulate further comprises a first aliphatic hydrocarbon wax, which is incorporated during the polymerization of the styrene/acrylic polymer. A second aliphatic hydrocarbon wax is mixed with the polymerized styrene/acrylic polymer containing the first aliphatic hydrocarbon wax after polymerization of the copolymer.
In one embodiment of the present invention, the first in-situ aliphatic hydrocarbon wax comprises a paraffin wax. In one exemplary embodiment, the paraffin wax has a melting point of from about 40xc2x0 C. to about 130xc2x0 C. More preferably, the paraffin wax has a melting point of from about 70xc2x0 C. to about 120xc2x0 C., and most preferably from about 80xc2x0 C. to about 110xc2x0 C. In another exemplary embodiment, the paraffin wax is of the formula CnH2n+2, wherein n ranges from about 12 to about 22, more preferably n is about 17.
In another embodiment of the present invention, the second external aliphatic hydrocarbon wax comprises a polyolefin wax. In one exemplary embodiment, the polyolefin wax has a melting point of from about 110xc2x0 C. to about 140xc2x0 C., more preferably from about 115xc2x0 C. to about 125xc2x0 C. In another exemplary embodiment, the polyolefin wax comprises polyethylene, polypropylene, a copolymer of an olefin and a styrene-malic anhydride half ester, or mixtures thereof.
In yet another embodiment of the present invention, the second aliphatic hydrocarbon wax comprises paraffin wax. In one exemplary embodiment, the paraffin wax is of the formula CnH2n+2, wherein n ranges from about 12 to about 22, more preferably n is about 17.
In another exemplary embodiment, the first aliphatic hydrocarbon wax has a molecular weight average range of from about 800 to about 1300 and a melting point of from about 70xc2x0 C. to about 120xc2x0 C. In another exemplary embodiment, the first aliphatic hydrocarbon wax has a wax domain as measured according to Scanning Electron Microscope (SEM) or Transmission Electron Microscope (TEM) of from about 0.1 micron to about 1.0 micron.
In one exemplary embodiment of the present invention, the second aliphatic hydrocarbon wax has a molecular weight average of from about 500 to about 4000. In still another exemplary embodiment, the second aliphatic hydrocarbon wax has a wax domain as measured according to SEM or TEM of from about 2 microns to about 5 microns.
In another embodiment of the present invention, the styrene/acrylic polymer has a bimodal molecular weight distribution comprising of at least 10% by weight, of polymer having a weight average molecular weight of from about 300,000 to about 1,000,000, and 90% or less by weight of polymer having a weight average molecular weight of about 40,000 or less.
In one embodiment of the present invention, the toner particulate comprises from about 0.5 to about 10 weight percent of, the first aliphatic hydrocarbon wax, and from about 1 to about 10 weight percent of the second aliphatic hydrocarbon wax. In another embodiment of the present invention, the styrene/acrylic copolymer and the first aliphatic hydrocarbon are combined in an amount of from about 90 to about 99 weight percent copolymer and from about 1 to about 10 weight percent of the first aliphatic hydrocarbon wax, based on the polymer and wax combined.
The toner composition may further comprise a magnetic component. Exemplary magnetic components may include magnetic pigments, metal oxides or mixtures thereof known in the art and typically employed in toner particulates. In one embodiment of the present invention, the toner particulate comprises iron oxide. Suitable iron oxides include magnetite, hematite, ferrite, and modified forms of such oxides. In one exemplary embodiment, the toner composition comprises, by weight, from about 5 to about 30 weight percent of the magnetic material.
The toner composition may further include one or more charge control agents which contribute to stabilization of the charge characteristics of the toner composition. In accordance with the present invention, the toner composition preferably is a negatively charged toner. Negatively-charged toner control agents include, but are not limited to, organic metal complexes or chelates of metals such as chromium, zinc, and/or iron, and aluminum complexes of an organic compound. Complexes or chelates of organic acids, azo compounds and the like are also suitable. In one embodiment of the present invention, the toner composition comprises an azo charge control agent, preferably a chromium azo charge control agent.
In one exemplary embodiment, the charge control agent is included in the toner composition in an amount sufficient to contribute to stabilization of the charge characteristics. In one embodiment of the present invention, the toner composition comprises, by weight, from about 0.1 to about 10%, preferably from about 0.25 to about 5%, more preferably from about 0.5 to about 2% and still more preferably about 1.5% of a charge control agent.
The toner particulates of the present invention are typically prepared as follows: the first aliphatic hydrocarbon wax is incorporated into the styrene/acrylic copolymer during polymerization of the styrene/acrylic copolymer. The second aliphatic hydrocarbon wax may thereafter be kneaded with the styrene/acrylic polymer containing the first aliphatic hydrocarbon wax. The resultant mixture is, for example, solidified, pulverized and temporarily classified to provide toner particulates of a desired size. Kneading may be performed with a heat-kneading machine such as a heat roller, a kneader or an extruder. Milling or pulverizing may be performed with any suitable crushing or grinding mill.
Typically toner particulates have a diameter in the range of from about 1 to about 50 microns, and more preferably in the range of from about 1 to about 25 microns, and still more preferably from about 6 to about 12 microns. A preferred particle size distribution is one wherein the median particle diameter size is the range of from about 6 microns to about 12 microns, more preferably in the range of from about 7 microns to about 11 microns.
As mentioned above, the first aliphatic hydrocarbon wax is incorporated into the styrene/acrylic copolymer during polymerization of the styrene/acrylic copolymer resin. In one embodiment, after polymerization, additional toner particulate ingredients may be mixed, sifted into an extruder and melt mixed with the polymer containing the first wax. The mixture coming out of the extruder may be solidified, for example, using an underwater pelletizer or chilled roller. The mixture may then be milled, for example, in an air jet mill, and classified to obtain toner particulates of the desired size.
The milled and classified toner particulates may be blended in a high speed blender with silicas, inorganic oxides and/or inorganic compounds. Suitable silicas include fumed silica and hydrophobically treated fumed silica. Preferably, the silica is a hydrophobically treated fumed silica. In one embodiment of the present invention, the resulting toner composition comprises the toner particulates with silica, inorganic oxides associated on the surface thereof and/or which may be present in the toner particulate surface.
In another embodiment of the present invention, the toner particulates are blended with silica, preferably hydrophobically treated fumed silica, and inorganic compounds. The toner particulates may be blended with from about 1.0% to about 1.2%, preferably about 1%, silica and from about 0.1% to about 3.0%, preferably 1%, inorganic compounds, by weight of the total toner composition.
In one embodiment, the toner composition comprises from about 40 to about 95 weight percent of the toner particulate. In another exemplary embodiment, the toner composition comprises from about 60 weight percent to about 85 weight percent of the toner particulate.
Typically, toner compositions comprising toner particulates in accordance with the invention are applied to substrates such as paper. In one embodiment, after application to the paper, the toner composition is heated and pressed. A fuser assembly having at least one rotating heat roller and at least one rotating pressure roller may be used for heating and pressing. The heat roller and pressure roller may be arranged in opposition to each other to form a nip. The paper is passed through the nip. Heat and pressure are applied as the paper passes through the rotating head and pressure rollers.
Generally heat is applied in the temperature range of at least of about 100xc2x0 C., more preferably from about 100xc2x0 C. to about 250xc2x0 C., even more preferably from about 140xc2x0 C. to about 190xc2x0 C., and most preferably from about 160xc2x0 C. to about 180xc2x0 C. In one exemplary embodiment, pressure may be applied in an amount of at least about 10 pounds per square inch, preferably from about 10 to about 30 pounds per square inch.